1. Field of the Invention
The present invention relates to a photocatalyst-coated body excellent in high weather resistance, hydrophilicity, harmful gas decomposability, and various coating characteristics in applications of exterior materials of buildings and the like; and a photocatalytic coating liquid for the same.
2. Description of Related Art
In recent years, a photocatalyst such as titanium oxide is being used for various applications such as exterior materials for buildings. By utilizing the photocatalyst, it is possible to decompose various harmful substances with light energy or to hydrophilize the substrate surface coated with a photocatalyst and easily wash away the stain adhered on the surface with water. As a technique to obtain the photocatalyst-coated body coated with such a photocatalyst, the followings are known.
A technique to impart hydrophilicity to the surface of a synthetic resin and the like using an aqueous dispersion comprising photocatalytic metal oxide particles, colloidal silica, and a surfactant is known (For example, Japanese Patent Laid-Open Publication No. H11-140432). In this technique, hydrophilicity is enhanced by adding the surfactant in an amount as large as 10 to 25% by weight. In addition, white turbidity due to the diffuse reflection of light is prevented by making the film thickness 0.4 μm or less.
A technique to obtain a photocatalytic body by forming a coated film comprising silica sol as a binder component and photocatalytic titanium dioxide on a substrate is also known (For example, Japanese Patent Laid-Open Publication No. H11-169727). In this technique, the amount of silica sol to be added is claimed to be 20 to 200 weight parts in terms of SiO2 relative to titanium dioxide, the content of titanium dioxide being high. In addition, the particle size of the silica sol is as small as 0.1 to 10 nm.
A technique to form a photocatalytic coating film which transmits 50% or more of light of a wavelength of 500 nm and blocks 80% or more of light of a wavelength of 320 nm using a photocatalytic paint is also known (For example, Japanese Patent Laid-Open Publication No. 2004-359902). In this technique, a partially hydrolyzed product of organosiloxane is used as a binder of the photocatalytic paint, the preferred amount of which to be added is claimed to be 5 to 40% by mass of the total paint composition.
In the meantime, there has been known a problem that, when the substrate of the photocatalytic layer is constructed with an organic material, the organic material is decomposed or deteriorates by photocatalytic activity of the photocatalyst. In order to cope with this problem, a technique is known to protect the substrate carrier from deterioration by photocatalytic action by providing an adhesive layer of a silicone-modified resin and the like between the photocatalytic layer and the carrier (For example, see WO 97/00134).